What is wrong with my vision, and what can I do?

Although there are many possible causes of glaucoma (e.g. trauma, inflammation, previous surgery, or an inherited tendency), it is usually possible to identify the mechanism of elevated IOP by careful history taking, anterior segment examination, and optic disc assessment using a slit lamp. After assessment, the clinician can group the glaucomatous optic neuropathies into three main categories: primary open-angle glaucoma (POAG), primary angle-closure glaucoma (ACG), and secondary glaucomas (including pseudoexfoliation, pigmentary, uveitic, lensinduced, neovascular, steroid-induced and traumatic). As a group, the glaucomas are chronic, life-long diseases, and it is therefore essential to collect and record clinical data accurately so that patients with progressive disease or who develop other ocular pathology can be identified at an early stage.


Introduction
The glaucomas are a group of progressive optic neuropathies associated with characteristic structural changes at the optic nerve head (cupping) and corresponding visual field defects.The main modifiable risk factor for glaucomatous optic neuropathy is increased intraocular pressure (IOP).The aims of assessment are: • accurate diagnosis • identification of the cause of increased IOP, if applicable • quantification of the level of glaucoma damage and functional impairment.
Although there are many possible causes of glaucoma (e.g.trauma, inflammation, previous surgery, or an inherited tendency), it is usually possible to identify the mechanism of elevated IOP by careful history taking, anterior segment examination, and optic disc assessment using a slit lamp.
As a group, the glaucomas are chronic, life-long diseases, and it is therefore essential to collect and record clinical data accurately so that patients with progressive disease or who develop other ocular pathology can be identified at an early stage.

History
Taking a careful history helps in two ways: 1 Identification of risk factors for glaucoma and glaucoma progression.The depth of the anterior chamber measured at the temporal limbus is a good indicator for the risk of angle closure.Van Herick's technique involves using a slit lamp to estimate the depth of the anterior chamber at the temporal limbus by comparing it with the peripheral thickness of the cornea at this point.
The technique should be performed in a standardised way so that results can be compared at different points in time or between patients.
The steps (Figure 1) 1 Explain to the patient what you are going to do.
2 Dim the lights in the room.3 Turn the illumination column of the slit lamp to the temporal side, away from the visual axis, by 60°.Some slit lamps can lock at this angle (Figure 1). 4 Shine the slit lamp beam from the side at the peripheral part of the cornea and iris (the limbus), where the anterior chamber and iris are just visible.The light must be perpendicular to the temporal limbus, as close as possible to the limbus.5 View the anterior chamber from the nasal side.6 Compare the depth of the anterior chamber with the peripheral corneal thickness (Figure 2).
If the depth of the temporal limbal chamber is less than a quarter of the peripheral corneal thickness, then there is a high likelihood (around 84%) that the person has an occludable angle in that eye.If the thickness of the temporal limbal chamber is less than 5% of the depth of the chamber, the likelihood that it is angle-closure glaucoma increases to around 91%.

Visual fields
Testing visual fields to confrontation with a red target (see page 68) can detect significant visual field defects.Simple measures such as tangent screen testing can be effective.Accurate assessment of visual field defects requires visual field perimetry: manual (Goldmann) or automated (Humphrey) perimetry techniquesgive detailed visual field data.The results of these are dependent on the experience and skill of the person doing the tests, however.

Slit lamp examination of the anterior segment
A systematic examination of the anterior segment ensures that all important clinical signs are observed.
Gonioscopy is very helpful, however, if a gonioscope is not available, the depth of the limbal anterior chamber can be estimated by Van      to assess it in cases of suspected glaucoma.Gonioscopy contributes answers to two questions: 1 What type of glaucoma is it?2 What is the risk of angle closure?
See the panel on page 51 for practical instructions.The morphology of the chamber angle can be classified using several systems.For example, the Shaffer classification grades morphology from 4 to 0, where: •

Tonometry
Accurate IOP measurement together with optic disc assessment is the backbone of diagnosis and management of glaucoma.IOP can be measured with applanation tonometry; this is still the gold standard, but it is difficult to get accurate readings unless the examiner is experienced. 1The applanation tonometer also needs to be calibrated regularly.Other instruments for measuring IOP include the Schiotz tonometer, the tonopen, and the non-contact 'airpuff' tonometer.Rebound tonometry may be also an alternative if applanation tonometry is not available, and is very useful in children or at mobile clinics. 2 Normal IOP is below 21 mmHg.However, be aware that patients who return for follow-up visits may remember to use their eye drops just before they come to the clinic, so that theassessed; ir IOP appears to be controlled.This means that the optic disc and visual fi elds must also be assessed; do not rely on IOP alone.

Ophthalmoscopy of the optic disc
Glaucomatous changes to the optic nerve head are central to diagnosing glaucoma and its progression.See page 55 for a detailed guide to identifying a glaucomatous optic nerve head.

Summary
Identifying and documenting the cause of glaucoma, as well as the resulting structural changes and functional loss, are key steps in assessing a patient with glaucoma.They allow the clinician to determine if there are any specific modifiable factors and provide information on the severity of the disease to guide the management decisions.

2
Identification of medical and social factors critical to optimum glaucoma management.Risk factors for glaucoma • High IOP • Age • Ethnicity (African: POAG, Asian: ACG) • Positive family history of glaucoma • Refractive status (myopia and hypermetropia) • Previous ocular trauma • Previous intraocular inflammation • Previous ocular surgery • Steroid usage.Risk factors for disease progression • Family history of glaucoma blindness • Severe visual loss at presentation • Previous history of high IOPs.medical factors in glaucoma management • Contra-indications to medications.For example, topical beta-blocker therapy (such as Timolol) is contra-indicated in people with asthma, chronic pulmonary glaucOma aSSESSmENT The next step: detailed assessment of an adult glaucoma patient Van Herick's technique, step by step

Further reading 1
Foster PJ, Devereux JG, Alsbirk PH, et al: Detection of gonioscopically occludable angles and primary angle closure glaucoma by estimation of limbal chamber depth in Asians: modified grading scheme.Br J Ophthalmol 2000; 84:186-192.

Figure 4 .
Figure 4. Open chamber angle of an African patient viewed with a gonioscope Cornea Oedema, scars (TG?), infiltrates, keratic precipitates (UG), central vertically distributed pigment deposits on the endothelium (Krukenberg spindle) (PG) Anterior chamber Depth (van Herick), cells (inflammation) (UG), hyphema, vitreous (TG) Iris Transillumination defects (PG), white flake-like material on the pupillary border, absent pupillary ruff, poor dilatation (XFG), pigment dispersion (PG, XFG), heterochromia, iris nodules, posterior synechiae, atrophy, anisocoria (UG), Neovascularisations of the iris (UG, NG) Gonioscopy 1° position Increased trabecular pigmentation (XFG; PG), debris and peripheral anterior synechiae (UG), fine white protein deposits (LG), trabecular neovascular membrane or fine neovascularisations (NG), angle recession, ghost cells, retained foreign body, cyclodialysis cleft (TG).Angle closure.Lens Luxation (TG), irido-phacodonesis (XFG), large lens, hypermature cataract (LG) Optic nerve head Macula Periphery Vertical cup-disc ratio, position of vessels, macular degeneration, diabetic retinopathy, retinal detachment, hypertensive retinopathy Easy-to-use, portable Icare tonometers are now available for IABP members.w w w .i c a r e t o n o m e t e r .c o m • i n f o @ i c a r e f i n l a n d .c o m Icare Finland Oy is an advanced medical technology company based in Helsinki Finland.Our product line consists of tonometers, specialized instruments for measuring Intra Ocular Pressure (IOP) with unique, patented rebound technology without anaesthesia.A D V E R T I S E M E N T Herick's test (see the panel opposite).See Table 1 overleaf for a standardised glaucoma assessment tool.